BACKGROUND: Vaping's popularity among adolescents has raised concerns about its potential role as a gateway to cigarette smoking. This study offers the first assessment of the relationship between vaping and subsequent cigarette smoking initiation among Australian adolescents and underscores potential methodological limitations in previous investigations in other countries.
METHODS: We conducted a retrospective cohort analysis of data from 5114 Australian adolescents aged 14-17 recalling information on smoking and vaping initiation from age 12 to 17. The outcome was smoking initiation, analysed with negative-binomial regression to estimate incidence rate ratios (IRRs) for vape-status (ever-vaped vs never-vaped) as a time-varying exposure. We also re-analysed using the methods of previous studies not accounting for the time-varying nature of e-cigarette exposure.
RESULTS: Participants (n=5114) were retrospectively followed for 20478 person-years. After adjusting for socio-demographic variables and proxy measures of common liabilities for vaping and smoking, the rate of smoking initiation for those who ever-vaped was nearly 5 times that of those who never-vaped (IRR=4.9; 95% confidence interval: [3.9, 6.0], p<0.001), with IRRs considerably higher at younger ages. Not accounting for the time-varying nature of e-cigarette exposure in re-analysis attenuated the estimated IRR by 44%.
CONCLUSIONS: Vaping markedly increases the risk of subsequent smoking initiation among Australian adolescents from age 12 to 17, with those initiate vaping earlier bearing an alarmingly disproportionate burden of the elevated risk. Additionally, the relative risk of future smoking due to vaping may have been underestimated in other studies due to methodological differences. Our findings are particularly significant as they highlight the need for public health interventions and strict e-cigarette access laws. The learnings from this study and it's methods are hugely relevant to the international tobacco control community and will support the development and implementation of evidence-based policy in other countries.